The invention relates to an improvement in a web former for a card or the like which produces a bat of textile fibers for the card.
In fiber blending systems and the like, textile fibers such as cotton and synthetic fibers are processed and pneumatically or otherwise supplied to a line of card machines. Each of these card machines has associated therewith a web former which forms the pneumatically fed fibers into a bat which is then supplied to the card and processed thereby. The web former may include within an interior chamber a shaker plate, e.g., as described in U.S. Pat. No. 4,009,803 and other patents. This shaker plate is oscillated by a motor to shake the fibers into an area in the bottom of the chamber from which they are pulled by rollers which form the fibers into a bat.
Should the card machine malfunction or cease operating for any reason, it is desirable that the shaker motor be immediately shut off. In the past, this has been done by providing a "knock-off" control which connects to the card by electrical, mechanical, or pneumatic means to provide a signal rendering the shaker motor inoperative when the card stops operation. On the other hand, it is desirable to delay shaking for a short time after start-up of the web former.
There are substantial disadvantages, however, in providing a mechanical, electrical, or other connection between the card and the shaker motor. Since the rollers which form the bat are controlled by the card and stopped when the card stops, the movement of these rollers can be sensed and the shaker motor turned off whenever motion of the three rollers ceases. The difficulty is that the rollers turn slowly, and it is difficult to get a reliable signal at slow speeds using conventional techniques such as magnets mounted on a gear. Because of the low speed, the magnetic signals produced are weak and the noise/signal ratio too large to provide reliable operation. Adjustments with magnetic devices are difficult and adjustments in the field are complicated.
Applicants, however, have discovered that the above problem can be resolved by optically encoding the rotation and in particular sticking a photographic negative having black bars (preferably 60 bars per revolution) on a clear, light transmitting plastic disc which rotates with any one of the rollers and detecting light which passes through the disc or is reflected therefrom. Such optical devices are usually found in high-speed high-frequency applications. In the present situation, however, such an encoder provides a suitable signal having a very low noise/signal ratio, the signal being a train of pulses.
The output of this encoder is applied to a circuit discussed in detail below. The pulses from the encoder set a one-shot multivibrator which times out after a predetermined time interval, e.g., 8 seconds, to reset a relay latch which renders inoperative a coil controlling the magnetics of the shaker motor to disable the same. When the rollers resume rotation, producing pulses, the pulses are counted by a counter circuit to set the latch and cause resumption of the operation of the shaker motor only after a predetermined delay. As noted above, it is desirable under certain circumstances to delay operation of the shaker until a certain amount of material has moved through the system.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.